Rapid response to:
John Launer: Thinking the unthinkable on Lucy Letby
BMJ 2023; 382 doi: https://doi.org/10.1136/bmj.p2197, published 26 September 2023, cite as: BMJ 2023;382:p2197
I am a coauthor of the report of the Royal Statistical Society https://rss.org.uk/news-publication/news-publications/2022/section-group-reports/rss-publishes-report-on-dealing-with-uncertainty-i/. It is deeply distressing that the police investigation into the case of Lucy Letby and the subsequent trial made all of the mistakes in our book. The jury was never told how the police investigation arrived at that list of “suspicious” events and how it was further narrowed down to the list of charges. This is a case in which a target was painted around a suspect by investigators. We call it confirmation bias, in statistics. It is also often referred to as the Texas sharpshooter paradox.
Thanks to amateurs who report their work on Twitter and YouTube, we now know how the list of charges in the Lucy Letby case evolved. It is utterly scandalous that this history was not revealed to the court. Here is the broad picture.
Doctors reported Lucy to the police, against the wishes of the hospital board.
They told the police the exact period she had been on the ward and gave them the files on all deaths in that period and on some of the incidents: namely, exactly and only those “arrests” at which Lucy had been present.
What qualifies as an incident, what is an arrest?
There is no medical category “arrest, resuscitation” under which such events are logged in hospital administration. Probably there were about five times as many such events when Lucy was not on duty, but nobody has ever looked. There is no medical definition of such an event. No formal criteria.
“Unexpected, unexplained, sudden” are also not defined in any formal way. Nor is “stable”.
Next the absolutely unqualified, long retired, paediatrician Dewi Evans, who has a business helping out in civil child custody cases, went through those medical files looking for anomalies about which he could fantasise a murder or murder attack. His ideas that milk was injected into the stomach or air into the veins were far fetched, and later not confirmed by any other evidence. On the contrary, the actual evidence certainly contradicts the idea that Lucy Letby actually attacked any child. He never gave alternative medical explanations, as would have been the obligation of a forensic scientist. All the deaths had had a post-mortem and a coroner’s report. Every single event on the charge sheet has absolutely normal explanation. Lucy was never seen doing anything wrong.
The medical experts for the prosecution merely confirmed Evans’ diagnosis, they also did not do the job of a forensic scientist.
The defence had no experts. They had brought in one paediatrician. But at the pre-trial hearing he said he wasn’t qualified in endocrinology, toxicology, etc etc etc.
This was Texas sharpshooter, big time. Plus utterly incompetent defence.
Member of Royal Dutch Academy of Sciences
Past president of Dutch statistical society.